There's an example on this site.
C# Sockets and Serialization[
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You might want to take a look at this library.
Lidgren networking library[
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The problem with a multiplayer racing game is that things go fast. You might get desync issue or cars that warp everywhere.
Multiplayer games usually implements algorithm that will interpolate player position with the "last received state".
I hope it helps, if the example I gave you aren't what you need, just tell me, I'll try more.